For formation of a thin film such as a silicon oxide layer on a substrate such as a semiconductor wafer (hereinafter, “wafer”), a film formation apparatus based on atomic layer reposition (ALD) is known in the art. In the film formation apparatus based on ALD, a plurality of wafers placed on a rotary table in a vacuum chamber is revolved by the rotary table so as to sequentially pass through a region to which a source gas is supplied and a region to which a reaction gas is supplied. In this apparatus, the source gas is supplied through a gas nozzle extending in a radial direction of the rotary table and having gas discharge holes formed in a longitudinal direction thereof. In order to improve in-plane uniformity of the film forming process by allowing the source gas to be adsorbed onto the wafer with high in-plane uniformity, the gas nozzle is required to be placed parallel to the wafer.
For example, a technique on a structure of mounting a gas nozzle has been known. In the technique, a sleeve is inserted into a through-hole formed through a sidewall of a process chamber, which is a vacuum chamber, from the outside of the process chamber, and a proximal end of a gas nozzle is inserted into the through-hole from the inside of the process chamber (a process space) to be engaged with an inner circumferential surface of the sleeve. Then, seal members (O-rings) are disposed at intervals in an axial direction between an outer circumferential surface of the proximal end of the gas nozzle and an inner circumferential surface of the sleeve to achieve hermetic sealing, and a process gas is supplied to the gas nozzle through a gas supply channel that is in fluid communication with the through-hole.
However, when the operation time of the film formation apparatus is lengthened, the seal members soften and the height of a leading end of the gas nozzle is lowered from an initial height thereof, thereby causing the gas nozzle to be microscopically deflected. Thus, there is a concern that it is difficult to maintain a low maintenance frequency.